PURPOSE: To increase the combustion efficiency of a burner, by recycling at least part of exhaust gas from a combustion zone to the side of combustion by an air ejector.

CONSTITUTION: The secondary combustion chamber 6 is directly connected to a kiln, and combustion air V4 is supplied to the chamber 6 by a blower B3. Part (VR) of exhaust gas V8 is joined to the secondary air V2 which flows through a flow path to a kiln, while the remainder gas is discharged unrecovered. A joint part 13 consists of an air ejector having a Venturi structure, so that reflux exhuast gas is sucked by the suction effect of the secondary air (VEJ) and is returned to a burner, being mixed with the secondary air V2. Part (VE) of exhaust gas is directly discharged into open air. In such a manner, the combustion efficiency of a burner can be increased.